1. Field of the Invention
The present invention relates to an optical photographing lens assembly, and more particularly, to a compact optical photographing lens assembly used in a portable electronic product.
2. Description of the Prior Art
The demand for compact imaging lenses has grown in recent years as the popularity of portable electronic products with the photographing function has increased, and the sensor of a general photographing camera is none other than CCD (charge coupled device) or CMOS (Complementary Metal Oxide Semiconductor Sensor). Furthermore, as advanced semiconductor manufacturing technology has allowed the pixel size of sensors to be reduced, and the resolution of compact imaging lenses has gradually increased, there is an increasing demand for compact imaging lenses featuring better image quality.
Generally, a conventional optical system for compact imaging lenses, such as the one disclosed in U.S. Pat. No. 7,145,736, is of a triplet type comprising, in order from the object side to the image side: a first lens element with positive refractive power; a second lens element with negative refractive power; and a third lens element with positive refractive power. As the popularity of high profile mobile devices such as smart phones and PDAs has led to a rapid increase in the resolution and image quality of compact imaging lenses, a conventional three-element lens has become insufficient for high-end imaging lens modules.
U.S. Pat. No. 7,365,920 has disclosed a four lens element assembly, wherein two spherical-surface glass lenses serving as the first and second lens elements are adhered together to form a doublet and thereby to correct the chromatic aberration. Such an arrangement of optical elements, however, has the following disadvantages: (1) the freedom of the system is curtailed due to the employment of excess number of spherical-surface glass lenses, thus the total track length of the system cannot be reduced easily; (2) the process of adhering glass lenses together is complicated, posing difficulties in manufacture. As there is an ongoing trend toward compact yet powerful electronic products, more compact imaging lenses with higher specification will be developed, that is, the lens elements must be arranged closer together in a relatively small space. However, such an arrangement may cause multiple reflections and refractions of the unwanted light within the lens assembly, compromising the image quality of the lens assembly.
Therefore, a need exists in the art for an optical photographing lens assembly that features better image quality, maintains a moderate total track length and is applicable to compact portable electronic products.